Methods to grow large crystals provide the foundation for material science and technology. Here we demonstrate single crystal homoepitaxy of a metal-organic framework (MOF) built of zinc, acetate and terephthalate ions, that encapsulate arrays of octahedral zinc dimethyl sulfoxide (DMSO) complex cations within its one-dimensional (1D) channels. The three-dimensional framework is built of two-dimensional Zn-terephthalate square lattices interconnected by anionic acetate pillars through diatomic zinc nodes. The charge of the anionic framework is neutralized by the 1D arrays of Zn ( DMSO ) 6 2 + cations that fill every second 1D channel of the framework. It is demonstrated that the repeatable and scalable epitaxy allows square cuboids of this charge-transfer MOF to grow stepwise to sizes in the centimeter range. The continuous growth with no size limits can be attributed to the ionic nature of the anionic framework with cationic 1D molecular fillers. These findings pave the way for epitaxial growth of bulk crystals of MOFs.

• Klíčová slova
• Organic-inorganic nanostructures,
• Publikační typ
• časopisecké články MeSH

Optical properties of molecules change drastically as a result of interactions with surrounding environments as observed in solutions, clusters, and aggregates. Here, we make 7,7,8,8-tetracyanoquinodimethane (TCNQ) highly luminescent by encapsulating it in crystalline melamine. Colored single crystals are synthesized by slow evaporation of aqueous tetrahydrofuran solutions of melamine and TCNQ. Single-crystal X-ray diffraction reveals the lattice structure of pure melamine, meaning that the color is of impurities. Both mass spectrometry and UV-vis spectroscopy combined with density-functional theory calculations elucidate that the impurity species are neutral TCNQ and its oxidation product, dicyano-p-toluoyl cyanide anion (DCTC-), whose concentrations in a melamine crystal can be controlled by adjusting the molar ratio between melamine and TCNQ in the precursor solution. Fluorescence excitation-emission wavelength mappings on the precursor solutions illustrate dominant emissions from DCTC- while the emission from TCNQ is quenched by the resonance energy transfer to DCTC-. On the contrary, TCNQ in crystalline melamine is a bright fluorophore whose emission wavelength centered at 450 nm with internal quantum yields as high as 19% and slow fluorescence lifetimes of about 2 ns. The method of encapsulating molecules into transparent melamine would make many other molecules fluorescent in solids.

• Publikační typ
• časopisecké články MeSH